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Old 20-09-2011, 21:07   #46
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Re: Aluminum vs Steel Dive Tanks

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Originally Posted by billwa View Post
Browsing this , I havent seen it mentioned that:

For any given mass of contained air, modern steel tanks (eg faber 12l 232 bar) are lighter and smaller than aluminium tanks which will hold an equivalent mass of air. I have yet to see any tank specification which is heavier in steel than in aluminium for same amount of air held.

So for the same length of dive duration, the steel tanks will be lighter on the surface.

I have a set of steel in the house, as I hate carrying too much weight to the car, to the boat ets.

As a side note:
On the boat, a have a set of ali - they dont rust.
Thanks billwa

OK, if I am only diving from the boat...

Have been getting a lot of flack from the scuba crowd about AL tanks for the reasons given, wetsuit, deep dives and it all is being related that I do not wear wetsuits, dive only in warm water and do not enjoy deep dives any more than shallower dives, but there is still the standard that's what everybody uses answer. I currently live in the mountains at over 7000 feet but have no desire to climb Everest. From what I have discovered after the tank purchase it is believed that my decision, as well as savings, was sound. And that doesn't happen very often. The other thing I am adding to my resume is spear fishing and THAT has drawn flames from another cruiser forum, is off topic and all I need to say about that here!

So thanks again and glad to be on this forum, so far...
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Old 21-09-2011, 04:07   #47
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Don't buy or use steel on a liveaboard. They need to be kept in climate controlled conditions when stored as any moisture forming in them will cause them to rust and then they are a pia to deal with.
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Old 21-09-2011, 06:20   #48
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Re: Aluminum vs Steel Dive Tanks

2012iffy said 'what has come to my knowledge bank is that steel tanks have a far greater differential from full to empty than aluminum'
I think you may have this the wrong way round. Aluminum tanks become positively buoyant as they empty.
However as has been said before Al are the ones to go for if on a boat.
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Old 21-09-2011, 09:19   #49
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Re: Aluminum vs Steel Dive Tanks

Am I missing something here?

80 cu.ft. steel tanks from scuba.com

Buoyancy Full = -9.0lbs
Buoyancy Empty = -3.0lbs

80 cu.ft. AL tanks from scuba.com

Buoyancy Full = -1.4lbs
Buoyancy Empty = 3.4lbs

This is specific to tanks of similar volume and I fully realize the difference in tank size but the steel tanks have an empty/full differential of 6 pounds whereas the AL tanks have a differential of only 2. Now the difference here is that the AL tanks are 'positively buoyant' and if one weights up for just a slight bit heavy for the dive one should, using breath control, be good to surface without the elevator effect. The steel tanks would certainly be desirable when using a wetsuit as they are still negatively buoyant and the wetsuit would become more positive as one surfaces.

Again, I do not care to do deep dives or to dive in cold water, which is why I am moving south as soon as I get a personal matter (divorce!) behind me. Diving without a BCD is not an option. Having some weight on is a plus in the event I should have to get a bit positive. I would rather take a soft weight out of my pocket and leave it on the bottom than have myself down there. The only instance that I can foresee at this time for diving with out a BCD is cleaning the bottom of your boat. Forgive me but safety is always a concern in an already dangerous activity.

Another reason the decision was made to liveaboard is to be able to dive on a whim. By that I mean simply that if all else is in place and I want to go for a dive I put on the gear and go. Do the dive and be done. To quote some of the Jamaican's I have had the pleasure to associate with, "No pressure, mon!". No pressure to do my 3 dives a day that is the regimen (Hate that word!) of most people.

So, though the tanks were purchased prior to checking out all the variables it is apparent that the purchase was a good one. Now if I can stretch out another 10-15 years out of this ol' hide maybe, just maybe there will be some relaxation prior to that imminent end.

Fair winds and lots of bubbles!
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Old 21-09-2011, 09:34   #50
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Re: Aluminum vs Steel Dive Tanks

This is like the steel vs wood hull thread. The best one is the one you like the best. Air weighs the same no matter which type of tank you use. 80 cubic feet of air weighs about 6 pounds. If you take it out of a steel tank it will the steel tank will about 6 pounds lighter.The same for aluminum. I have been 225+ feet deep with steel and aluminum many times and dont really care which one I dive with. If the tank will hold the gass I need I'll dive it. To each his own.
I'm teaching a night navagation class this weekend, some are using steel and others are diving aluminum, its really not an issue. Just keep diving and having fun..
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Old 21-09-2011, 09:42   #51
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Re: Aluminum vs Steel Dive Tanks

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Originally Posted by Matt sachs View Post
This is like the steel vs wood hull thread. The best one is the one you like the best. Air weighs the same no matter which type of tank you use. 80 cubic feet of air weighs about 6 pounds. If you take it out of a steel tank it will the steel tank will about 6 pounds lighter.The same for aluminum. I have been 225+ feet deep with steel and aluminum many times and dont really care which one I dive with. If the tank will hold the gass I need I'll dive it. To each his own.
I'm teaching a night navagation class this weekend, some are using steel and others are diving aluminum, its really not an issue. Just keep diving and having fun..
Exactly. As long as you are properly weighted, not too much or too little which means:

1. you can be slightly negative at the end of the dive so you can do deco or safety stop at 20'

2. you have easily ditchable weight in some form so you can become positively buoyant at depth at the beginning of the dive

If you can accomplish these requirements with either tank then use the ones you like, steel or Al.
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Old 21-09-2011, 11:04   #52
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Re: Aluminum vs Steel Dive Tanks

Didn't a set of AL tanks blow up recently?
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Old 21-09-2011, 11:16   #53
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Re: Aluminum vs Steel Dive Tanks

Yes. In St Pete FL. Article here.

St. Pete veteran killed by exploding scuba tank | TBO.com

I have heard of 2 or 3 tank explosions in the last 10-12 years. Have not heard the analysis of the latest but previous explosions were traced to a bad alloy used in some Al tanks manufactured years ago (1970s??) by Luxfer and possibly others. Dive shops worldwide were notified and should not recertify or fill these tanks.
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Old 21-09-2011, 11:20   #54
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Re: Aluminum vs Steel Dive Tanks

Quote:
Originally Posted by 2012iffy View Post
Am I missing something here?

80 cu.ft. steel tanks from scuba.com

Buoyancy Full = -9.0lbs
Buoyancy Empty = -3.0lbs

80 cu.ft. AL tanks from scuba.com

Buoyancy Full = -1.4lbs
Buoyancy Empty = 3.4lbs

This is specific to tanks of similar volume and I fully realize the difference in tank size but the steel tanks have an empty/full differential of 6 pounds whereas the AL tanks have a differential of only 2

....
What you are missing is that the difference between a negative 1.4 and positive 3.4 is 5.8lbs.

Here's a table I found:

Code:
                           Actual     Empty    Buoyancy   Buoyancy   Buoyancy
Brand/Model    Pressure    Capacity   Weight   Empty      Full       Change  
                                                                             
Aluminum                                                                     
Luxfer 80      3000        77.4       31.38      4.4      -1.4       5.8     
Luxfer S80     3000        78.2       35.12      2.26     -3.6       5.86    
Catalina S80   3000        77.4       31.6       4        -1.8       5.8     
Catalina C80   3300        77.4       34.4      -0.2      -5.9       6.1     
                                                                             
Steel                                                                        
Faber 80       2400 +10%   78         30        -1.7      -7.55      5.85    
Faber 80       3180 +10%   80         32.5      -7.22     -13.22     6       
PST E7-80      3442 PSI    80         28        -2.5      -8.5       6       
PST LP-80      2400 +10%   80.6       34        -1        -7         6       
PST 80         3500        82         28.6      -3.3      -9.3       6
If you notice, the "Buoyancy Change" column changes in direct relationship to the "Actual Capacity" column. The Luxfer S80 and Faber 80 (2400psi) are almost identical capacity and buoyancy difference.

So, looks like to me the differential is identical between steel and aluminum tanks.

-dan
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Old 21-09-2011, 11:41   #55
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Re: Aluminum vs Steel Dive Tanks

Just got an update from a friend in the business on the tank explosion in St Pete. The tank was filled with 100% oxygen and there is debate as to the cause of the explosion. Tank could have been dropped on the valve, causing a spark and simultaneously releasing oxygen. Still would require some fuel for the oxygen, possibly a dirty, oily tank from a bad fill.

Theoretically you can generate enough heat to ignite oxygen/fuel mix from adiabatic compression by rapidly opening a tank valve but the current understanding is the explosion happened while the tank was being carried from one location to another, hence the speculation that it was dropped.
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Old 21-09-2011, 12:22   #56
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Re: Aluminum vs Steel Dive Tanks

"Don't buy or use steel on a liveaboard. They need to be kept in climate controlled conditions when stored as any moisture forming in them will cause them to rust and then they are a pia to deal with."


The outside enviroment does not effect the inside a scuba tank unless the compressor filling it has inadiquate filtering, or you leave it laying around with no valve on it, neither case is recomended nor should be practiced.
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Old 21-09-2011, 12:46   #57
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Re: Aluminum vs Steel Dive Tanks

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Originally Posted by Dulcesuenos View Post
Don't buy or use steel on a liveaboard. They need to be kept in climate controlled conditions when stored as any moisture forming in them will cause them to rust and then they are a pia to deal with.
You should never drain a tank completely. If you follow this rule, then moisture will never form in tanks while stored, regardless of what environment you store them in.
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Old 21-09-2011, 12:54   #58
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Re: Aluminum vs Steel Dive Tanks

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Originally Posted by Matt sachs View Post
This is like the steel vs wood hull thread. The best one is the one you like the best. Air weighs the same no matter which type of tank you use. 80 cubic feet of air weighs about 6 pounds. If you take it out of a steel tank it will the steel tank will about 6 pounds lighter.The same for aluminum. I have been 225+ feet deep with steel and aluminum many times and dont really care which one I dive with. If the tank will hold the gass I need I'll dive it. To each his own.

I agree with Matt. The difference is insignificant and you can (or should be able to) adapt very easily to either. I’ve dove small AL 40 tanks all the way to steel twin HP 130’s (100’s of dives on those). Talk about negative buoyancy. All-in-all, the only consideration I would give would be high pressure vs low, as not all fill stations can/will do high pressure fills (resulting in less volume for you), but low pressure tanks are bigger and take more space.

I dive a rebreather too, but it is probably not relevant to this thread which is about AL vs Steel. I suspect very few people on this forum use (or care to use) them as it is even a small percentage for the diving community, let alone the boating folks here in which not all dive. That topic is probably best left to the other forums or at least its own thread as it raises all sorts of other issues. And FYI for the one who asked.....my trimix dives are about $10 ea compared to $90 for others I dive with who use all OC. Not to mention the lessened deco time. They do have a place. Just not here.

As far as the explosion, it happens with steel and AL and is especially risky with 100% O2 and usually during the filling process. Not really relevant to the type of tank on board issue, and probably shouldn’t be used in consideration for what you are looking for. If you’re using high O2 gas, you won’t likely be asking advice here on what type cylinders you need.

Dive what is available and what works for you, but I wouldn't fret over the material. (Just my 2cts).
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Old 21-09-2011, 14:49   #59
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If you have a compressor on board great your tanks will always have air. Im sure the "experts here" always have enough air in their tanks when they are done diving to avoid moisture. Though for some reason I continually see divers with little or no air left for whatever reason. Do this for any length of time away from a compressor with steel and u will be tumbling your tanks. Just saying.......
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Old 21-09-2011, 17:40   #60
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Re: Aluminum vs Steel Dive Tanks

Steel tanks need tumbling after a few years anyway. No compressor gets all the water out the air and the pressure drop inside from simply using the tank causes slight condensation. Inconvenient, but I prefer to dive steel so I put up with it. I do miss the lower maintainance of my old aluminum 80's.
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